This invention relates to an apparatus and a method for driving a synchronous motor.
Synchronous motors have recently been used as fan motors for use with air conditioners and hot water suppliers, which are well adapted for the control of rotational speeds over a wide range, the economy of consumed electric energy and the suppression of mechanical noise. Also, such synchronous motors have been driven by suitable motor drive apparatuses.
Usually, Hall ICs (integrated circuits) as position sensors having a simple structure and being most inexpensive are incorporated in a synchronous motor. The Hall IC detects the positions of the magnetic poles of the synchronous motor so that the synchronous motor is driven by applying appropriate voltages across its windings accordingly. Further, the polarities of currents flowing though the windings of the synchronous motor are detected. The phase difference obtained from the data on the current polarities and the magnetic pole positions detected by the Hall IC, is controlled to achieve high efficiency drive.
JP-A-2006-34086 discloses a conventional drive apparatus for a synchronous motor.
Power is fed to the conventional drive apparatus from a DC power source. Current flowing from the DC source into the synchronous motor is detected, and there is generated a current signal corresponding to the peak value of the detected current. The difference signal obtained by subtracting the current signal from the externally inputted torque command signal (command signal for current value) is outputted. The position sensors deliver the position sensor signals having a constant phase relationship with respect to the voltages induced across the plural phase windings on the stator of the motor. The sinusoidal signals are generated whose voltage values change periodically according to the phase relationships. The amplitudes of the sinusoidal signals are determined depending on the above mentioned difference signal.
On the other hand, the phases of the currents flowing through the phase windings on the stator are detected, the phase differences between the position sensor signals and the current phase signals are detected, and the phase of the sinusoidal signal to be generated according to the phase of the position sensor signal is corrected on the basis of the phase difference.
A drive signal is generated by using a well-known PWM control, on the basis of the amplitude and the phase of the thus obtained sinusoidal signal, and the switching elements of the inverter are driven by supplying the sinusoidal signals to the gate drive circuit.
Namely, according to the synchronous motor drive apparatus disclosed in JP-A-2006-34086, the amplitudes of the voltages applied across the stator windings are determined in accordance with the difference between the current signal corresponding to the peak value of the current flowing from the power source into the motor and the externally inputted torque command signal. Then, the motor is driven by determining the phases of the voltages applied across the stator windings on the basis of the phase differences between the position sensor signals and the phase currents.